The invention relates the field of display devices for reproducing optical information. In particular, the invention relates to a display device based on the use of liquids for visualizing information, as well as an associated method.
From the prior art there is known an almost overwhelming variety of display devices serving the reproduction of optical information, such as e.g. text, still images or even moving images (videos). While a large proportion of these display devices serves in particular to reproduce multi-colored and quickly varying information, solutions exist which focus on the reproduction of more static and optionally monochrome information.
As an example for such display devices, reference is made to the technology of “electronic paper” developed by the company E-Ink (Cambridge, Mass./USA; www.eink.com). The document U.S. Pat. No. 6,120,588 (“Electronically addressable microencapsulated ink and display thereof”) is mentioned in this respect. Herein, a plurality of tiny globules is used which can be oriented in an electrical field and which are, for example, colored in white and black in equal share. By specific application of certain display areas with a corresponding electrical field these areas appear to be colored, whereas other areas appear uncolored. To enhance contrast, an opposed electrical field can be applied to the remaining areas. In particular advantageous is the fact that such devices can be operated with low power, however, they offer slow reaction times and moreover the disadvantage that only a few colors can be displayed.
The problem of high energy consumption is encountered, for example, by document U.S. Pat. No. 7,304,786 owned by the company Liquavista (NL). The display principle described therein is based on use of colored liquids, more specifically of a two phase mixture made up of colored liquid (oil) and a carrier liquid (water). Switching of a single image dot occurs by means of the effect of electrowetting. By utilizing the effect of electrowetting, energy input can be dramatically lowered in particular during the representation of static information, since energy is consumed only for changing, but not for holding a color. However, such displays are suitable, on the one hand, only for operation at normal ambient temperature, on the other hand, the technology described in this document is reliable only up to a certain pixel size, so that in particular large area displays cannot be realized with such a technique. Moreover, the pixels include merely a single color, so that display of plural different colors can only be achieved by means of a close arrangement of differently colored “sub-pixels” and use of optical fusion thereof to perceive one pixel.
As substantial disadvantage of display devices which are based exclusively on the effect of electrowetting, wherein thus the entire energy change the image impression results from this effect, is founded in that these forces are very low, so that correspondingly high electrical fields are necessary to bring large liquid volumes safely into a desired display condition. Simultaneously, these display devices often use display elements (“pixels”) comprising two chambers, one of them serving as a display, whereas the other one is used as a reservoir in case that the corresponding pixel is not to be displayed at the moment. These constructions are complex as well as error-prone; moreover, the magnitude of the electrical field to be generated is limited, since otherwise the dielectric strength of the used materials is exceeded by too high voltages. Solutions which utilize pumps to provide an increased liquid transport volume, can rarely be realized, since either a plurality of pumps were necessary or correspondingly complex switching valves had to enable a selection of the pixel which is to be driven, resulting in particular to extremely long switching times for an image often comprised of many thousands of pixels.
U.S. Pat. No. 3,566,172 A discloses a fluidic display including a display liquid for displaying information as well as a fluid feeding mechanism for delivering said at least one display fluid. Further, a common main duct is provided between at least one fluid reservoir and said fluid feeding mechanism.
EP 1 065 378 A2 discloses a microvalve and pump system as well as a method for manufacturing the same. The systems as described consist essentially of stacked elastic and inelastic layers, wherein a pair of adjacent layers forms an elastically deformable duct.
DE 697 11 750 T2 discloses an electrocapillary display sheet which uses several sets of reservoirs each holding a polar liquid of different color. By selectively activating the fluids of each set of reservoirs, at least one of the fluids from the set of reservoirs flows into a space which is shared by the fluids of this set of reservoirs to create a colored image dot.